lint: enable intrange linter (#7331)

Enable intrange linter to enforce modern Go range syntax over
traditional for loops, by converting:

for i := 0; i < n; i++

to:

for i := range n

Adding type conversions where needed for compatibility
with existing uint64 parameters.

Signed-off-by: Ville Vesilehto <ville@vesilehto.fi>

plugin/forward/setup.go

@@ -176,7 +176,7 @@ func parseBlock(c *caddy.Controller, f *Forward) error {
 		if len(ignore) == 0 {
 			return c.ArgErr()
 		}
-		for i := 0; i < len(ignore); i++ {
+		for i := range ignore {
 			f.ignored = append(f.ignored, plugin.Host(ignore[i]).NormalizeExact()...)
 		}
 	case "max_fails":